To ensure precise measurements, with no need for long, painstaking calibration procedures whenever the measuring tool is fitted to the measuring head, the connecting assembly must provide for repeatable, unmistakable positioning of the tool with respect to the head.
For this purpose, connecting assemblies are known comprising first supporting elements carried by the measuring tool; second supporting elements carried by an output member of the measuring head and cooperating with the first supporting elements to accurately define the position of the tool with respect to the measuring head; and releasable locking members for maintaining the tool and head in said position. Since the locking members normally require the use of tools to lock and release the measuring tool, assembly and disassembly of the measuring tool are relatively long, painstaking jobs.
Magnetic connecting assemblies between the tool and the output member of the measuring head are also known, which provide for relatively fast assembly and disassembly of the tool, but are affected by any external magnetic fields or dirt.
Moreover, magnetic connections require an extensive interaction region between the output member and the tool, so that the exchanged forces distributed over the entire interaction region have a fairly long arm with respect to the axis of rotation of the output member, and which produces interaction moments which make it difficult to ensure perfectly repeatable support of the tool on the head.